No Reinforcements

This achievement is easier to complete if you have 2 players. One player can stay on Azmodan in order to ensure he dies quickly while the other will stay near the center of the map to kill any Demon Gates that spawn.

If you are soloing this fight, try to stay near the center of the room as much as possible while damaging Azmodan. If you see any Demon Gates spawn, prioritize killing those first.

You can tell where a Demon Gate has spawned by looking at your mini-map if it is out of your field of view.